Recently, in the treatment of malignant tumors, a method in which a transformed anaerobic bacterium is used as a gene transfer carrier has been attracting attention; for example, a method in which a gene expressing a nitroreductase, which is an enzyme that converts a prodrug for an antitumor substance into the antitumor substance, is transported to a tumor site using a transformed clostridium has been proposed (ref. Patent Documents 1 to 3).
However, all of the microorganisms that have conventionally been used for the above-mentioned purpose are low toxicity mutants of pathogenic microbes, and the possibility of reverse mutation, with them returning to the original pathogenic microbes and exhibiting toxicity, cannot be ruled out; furthermore, due to mobility and invasiveness there is a possibility that the effect will be exhibited not only in diseased tissue but also in normal tissue to thus cause systemic side effect symptoms, and there is a problem in terms of safety.
Under such circumstances, Bifidobacterium, which is a nonpathogenic enterobacterium that is present within and makes up the flora in the human intestine and is known to be a very safe obligately anaerobic bacterium, has been attracting attention, and a transformed Bifidobacterium that expresses cytosine deaminase, which is an enzyme that converts 5-fluorocytosine, which is a prodrug for the antitumor substance 5-fluorouracil, into 5-FU has been developed (ref. Patent Documents 4 and 5).
This transformant Bifidobacterium has the advantage that when it is intravenously administered into an animal model of solid tumor which is an anaerobic disease, it specifically colonizes and grows in anaerobic diseased tissue in a low oxygen state and quickly disappears in normal tissue that is not in an anaerobic environment (ref. Non-Patent Documents 1 and 2).
In the meantime, in the treatment of an ischemic disease, in particular the treatment of a serious case of ischemia, an angiogenic therapy in which blood flow is restored by regeneration of blood vessels or development of collateral circulation has been attempted. Angiogenic therapy can be broadly divided into three types of therapies, that is, cell transplantation, protein administration, and gene therapy, but from the viewpoint of low invasiveness, gene therapy has particularly been attracting attention in recent years. In angiogenesis by gene therapy, for example, a gene coding for hepatocyte growth factor: HGF, vascular endothelial growth factor: VEGF, etc. is introduced into an area around an affected part by intramuscular injection or intraarterial infusion, thus promoting angiogenesis in the area around the affected part and thereby restoring blood flow (ref. e.g. Non-Patent Documents 3 and 4).
These angiogenesis therapies have been attracting attention as one option for a patient for whom revascularization is not possible or whom the effect is insufficient due to a disorder at the arteriolar level, or a patient who cannot be treated surgically due to a problem with invasiveness and, in particular, with regard to angiogenic therapy by gene therapy, many clinical tests have been carried out in recent years.